quality driven...2015/10/13 · see the difference 1 quality-driven: automotive display testing ©...

1 S E E T H E D I F F E R E N C E © 2015 Radiant Vision Systems, LLC. All Rights Reserved Quality-Driven: Automotive Display Testing

QUALITY DRIVEN - AUTOMOTIVE DISPLAY TESTING

Presented by Daniel van Brecht

2 S E E T H E D I F F E R E N C E © 2015 Radiant Vision Systems, LLC. All Rights Reserved

Agenda

• Introducing Radiant Vision Systems

• Automotive Test Solutions

• Automotive Display Testing

– Measurement Setup

– Analysis Capabilities

• Mura Testing

• Black Mura Measurement Standard

Quality-Driven: Automotive Display Testing


Quantifying Human Visual Perception

Radiant Vision Systems’ imaging hardware and software

replicate and quantify human perception

of brightness, color and scatter



A Konica Minolta Company



Head-Up Displays Instrument Panels Displays

Materials & Finishes Interior Lighting Exterior Lighting

Automotive Applications - Overview



Automotive Display Testing


High-quality perception of the

display under harsh environmental

conditions (over a long life-time)

• Temperatures -20°F to 185°F

• Read at nighttime and in sunlight

The Automotive Challenge

Dark-state displays are used to

minimize distraction and preserve the

dark-adaptation of the eye (nighttime)



“You See Everything on a Dark Display”

LCD blocking a bright backlight

Dark-Adapted Eye

Display defects cause high-contrast artifacts that are easily spotted by the dark-adapted eye



Non-Uniformity

(Color &

Brightness)

Pixel & Line Defects

Mura Image Sticking View Angle

Common Display Tests

Light Leakage

Color Offset Brightness Offset

Lv



Automotive Display Test Setup

Colorimeter or

Photometer

PC

DVI/LVDS Converter

& interface

DUT Secondary Display to PC

Dark Room



TrueTest™ Software for OEMs & Suppliers

Developed with the needs of OEMs & Suppliers in mind

• Many analysis tools

• Customization of tests

• Control of external devices

• Include home-brew analysis tools

• LabVIEW, Matlab, .NET API control

• 1-button control (Operator Mode)

• Fast testing

• Serial number tracking

• Report generation

R&D / Engineering Production Testing

Common language between OEMs & Suppliers



Defect Testing

Gradient

Line Defects

Particle Defects

Pixel Defects

Mura Testing

Color Edge Mura

Color Mura

Diagonal Pattern Mura

Polarizer Deformation

Spot Pattern Mura

Automotive Black Mura

Black Mura

Blob Analysis

Butterfly Mura

Corner Light

Diagonal Line Mura

Edge Mura

LED Mura

Line Mura

Random Mura

Spot Mura

TrueMURATest

General Display Testing

ANSI Brightness

ANSI Color Uniformity

Checkerboard Contrast

Chromaticity

Compare Points Of Interest

Distortion

Focus Uniformity

Points Of Interest

Uniformity

Tru

eM

ura

Plu

g-In

Standard Test Functions



Automatic Detection of the Active Display Area

Automatic Correction of the

Display Orientation

Automatic Image Crop Isolates

the Active Display Area

For All Analysis Functions Simple Positioning of the Device Under Test (DUT)



For All Analysis Functions Measuring Without Moiré Interference

Automated Moiré Removal

after Moiré removal

before Moiré removal



Pass / Fail

Pass / Fail

Pass / Fail

Pass / Fail

Pass / Fail

Start Test for Serial#

Add Data to Report

1

2

3

4

Test Luminance

Test Uniformity

Test for Black Mura

Test for Dead, or Stuck Pixels

5 Test Image Sticking

For All Analysis Functions Compose a Test Sequence



Application Highlight Mura Testing


Display Mura

Mura

• “Mura” is Japanese for “blemish”

• Local (gradual) increase/decrease in

luminance – or “blob”

• Often a subtle gradient on-top of an

unnoticeable large scale gradient

• Noticeability is highly subjective,

therefore difficult to test reliably by

humans

Luminance



• Defect or stress in one or more

layers

• Non-uniformity in bonding

(e.g. air bubble)

• Cleaning wipes / finger prints

• Light creep around

layers, leaking in from

the edges

• Pressure applied by the

display casing

• Stress applied by

deformation of the display

module

Common Causes of Mura

• Particle inclusion / scratch / fibers

• Backlight non-uniformity



Blobs Corner Mura

Clustered Mura Line Mura Large Scale Mura LED Mura Spot Mura

Many Flavors of Mura

• Each Mura type has its own

characteristics and requires a specific

analysis algorithm to test

• Often a combination of different Mura

are present

Edge Mura



Corporate Quality Standard

Qu

an

tifi

ed

Mu

ra Often driven by

• Marketing

• Sr. Management

• Customer Complaints

• Cost of avoiding

Objections to specific mura types may

vary over time



Mura Testing with TrueTest™

• Isolate Different Types of Mura



4 8

8 7

• Isolate Different Types of Mura

• Score the Different Mura




4 8

8 7

• Isolate different types of Mura

• Score the different Mura

• Pass/Fail test the different Mura




1. Measurement Image

Displays often have small gradients (Mura) on-top of

a large gradual slope

2. Local Contrast Image

Remove the large-scale gradients (and/or noise)

from the Measurement Image

Four Ingredients of Mura Analysis

Local Contrast Luminance



3. Standard Spatial Observer

Optionally, the Local Contrast Image can be

processed by an algorithm that describes a

Standard Spatial Observer

4. Weighting Mura Defects

Analysis with Weighting & Filtering of different

types of Mura defects

Four Ingredients of Mura Analysis

Spatial Observer

Noticeability Noticeability

- +



Filter Mura on local

contrast value

Distinction between

bright and dark Mura

Filter on Mura surface

area

Filter Mura on position

in the image

Filter on Mura shape

(circularity / line shape)

Filter on color

Cx, Cy

+ -

Treat groups of Mura

as a single defects

Filtering & Weighting Mura Defects



1

2

3

4

Black Mura

Edge Mura

Spot Mura

Line Mura

5 Corner Mura

FAIL

FAIL

TEST SEQUENCE

Mura Testing in TrueTest™

• Specialized analysis for each Mura type

• MAKRO style testing of the whole Mura spectrum

• Pass/Fail testing for each Mura type

• Export of (quantified) test values for statistical analysis



Black Mura consists of large blemishes grouped

together. TrueTest™ finds the mura, highlights it and

quantifies it. Quantification can be in local contract ratio,

JND or a customer specific manner

Butterfly Mura consists of blemishes in the corners

that are bright (or dark) compared to the edges. Here

the butterfly mura is shown on a “local contrast” image

TrueTest™ Examples



LED Mura consists of bright, evenly spaced blemishes

at one edge of the display. They often vary in shape

Edge Mura are bright blemishes on the edges of the

display that is easily seen when the display is dim.

TrueTest ™ Examples



Spot Mura are circular or non-circular blemishes. One

criteria for the test is the circularity of the blemish. In

this example only circular blemishes are considered

mura.

Light Leakage consists of different size bright areas

near the edge of the display. They typically appear

when the display is set to black or a very dark pattern.

This is typically the result of mechanical stress in the LCD

layer.

TrueTest ™ Examples



The Corner Mura test will only look for a bright

blemish in the corner that is more easily detectable with

the human eye when the display is dim. This may occur

when the LCD is pressed upon by the display casing, but

could have other root causes

Diagonal Line Mura (or diagonal band mura) is an

extended blemish that can be oriented in any direction.

This analysis can also be used for “rubbing mura” and

could potentially be set to only look for lines in a

specific angular span.

TrueTest™ Examples



Mura Testing to Human Perception

PASS



Mura Noticeability Factors

Mura Context

• Local contrast of the Mura

defect

• Mura Size, Shape, Orientation

• Position on the display

• Neighboring Mura

• Display size

Inspector Context

• Experience (perceptual

learning)

• Light & Color Sensitivity

• Mental state (e.g. fatigue)

• Environment (e.g. room

illumination)

• Yield pressure



1-Person Quality Judgment

• Large judgment error



Group-Average Quality Judgment

• Reduced judgment error

• Expensive



Displays sorted to quality

TrueTest™ Matching Human Judgment

Group-Average Quality Judgment

Matched TrueTest™ Judgment

Mura Test Parameters



Fine-Tuning

of Pass/Fail

1-Person Quality Judgment

Precise Scoring of Display Quality

TrueTest™

Display Quality Distribution



Time

Trending Display Quality Over Time

Exported data allows

trending display quality

Tracing mura defects to

changes in production



• Quality judgment equivalent to a group of human inspectors

• Low cost

• Repeatable test results

• High-consistency between test setups

• Common quality judgment between OEM & Supplier

• Fine-tuning of Pass/Fail criteria

• Easily scalable to high-volume testing

• Statistical analysis on different display defects

• Easily adaptable to a change in Quality Requirements

Benefits of TrueTest™ Mura Inspection



Testing to the Black Mura Standard



Standard Body: the German “Automotive working group displays” –

i.e. a collaboration between BMW, Volkswagen, Audi,

Daimler and Porsche

TrueTest™: Testing to the Black Mura standard is adopted in

TrueTest™ software

Distribution: The measurement standard is available through the

German Flat Panel Display Forum (DFF /

www.displayforum.de)

Content: Uniformity measurement standard for Displays

Black Mura Standard



Objectives of the Standard

• Open Standard

The test method is available to everyone

• No Preferred Equipment Supplier

The test can be performed with test

instruments available from various suppliers

• Simple Interpretation

The test method should be easy to

understand, i.e. the standard document

speaks for itself



Display Pixels

Slope

Avg. Luminance Luminance Gradient is obtained by the derivative of

the Luminance image

Xslope

Gradient

The Luminance Gradient in any direction is

approximated by 𝑋𝑠𝑙𝑜𝑝𝑒2 + 𝑌𝑠𝑙𝑜𝑝𝑒

2 Yslope

Test Method Outline



Assuming Weber’s Law is Applicable

∆𝑾𝒏𝒐𝒕𝒊𝒄𝒆

𝑾= 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡

Test Method Outline

• Small increment on a small load : noticeable

• Same increment on a large load : may not be not noticeable

The maximum (relative) gradient is searched for both a bright- and dark-state display

𝑳𝒈𝒓𝒂𝒅𝒊𝒆𝒏𝒕

𝑳 𝑚𝑎𝑥

𝑳𝒈𝒓𝒂𝒅𝒊𝒆𝒏𝒕

𝑳 𝑚𝑎𝑥



Gradient in y-direction Gradient in x-direction

Black Mura in TrueTest™

Pass / Fail test on :

• Average Luminance (Bright State

Display)

• Contrast Ratio (Bright vs. Dark)

• Max. gradient relative to white

• Max. gradient relative to black

Black Mura Image



1

2

3

4

Dead Pixels

Uniformity

Black Mura Gradient

Checkerboard Contrast

5 Corner Mura

TEST SEQUENCE

One Doesn’t Exclude the Other

Black Mura as part of a more elaborate display test



Comparing Mura Test Methods

Black Mura

• Analysis method is open and well documented

• Measurement Standard, i.e. the same for

everyone

• Not exclusive to Radiant, or any other supplier

of photometry equipment

• Available in TrueTest™ software

Radiant Developed Mura Testing

• Analysis method exclusive to TrueTest™ software

• User adjustable & configurable

• Elaborate Mura testing




display pixels

Lum

inan

ce

• Testing Mura + Background Gradient

• Error is limited by display uniformity

requirement

display pixels

Co

ntr

ast

• Testing Mura only

• Large-scale gradients are not noticeable

• Mura analysis is performed on a Local Contrast

Image

Black Mura Radiant Developed Mura Testing




• Adjustable sensitivity to different Mura types

• Allows correlation to Human Inspectors

• No differentiation between different Mura types

• Spatial observer not included

• Unwanted Pass / Fail

Same Gradient / Same Quality Same Gradient / Different Quality




Black Mura


• Rotation correction of the display area through image

processing

• Convenient positioning of the DUT

• Deliberate misalignment can reduce Moiré

• XY-axis alignment required between display and CCD

pixel grid

• Time consuming

X

Y

Radiant Developed Mura Testing




• Moiré removal by defocusing • Moiré removal by Dynamic Filtering

• Analysis on a sharp image

• Image can be used for high-resolution analysis (e.g.

testing for dead pixels)



http://upload.wikimedia.org/wikipedia/commons/9/9e/Bottle_Softfocus_0.jpg

http://upload.wikimedia.org/wikipedia/commons/e/ee/Bottle_Softfocus_2.jpg




Summary

• Radiant offers solutions for various Automotive Applications

• TrueTest™ software offers a total solution for display testing (OEMs & Suppliers)

• Many flavors of Mura

• Specialized Mura analysis functions

• 4 ingredients of Mura testing

• Matching TrueTest ™ to Group-Average Human Inspection

• Precise grading and trending of display quality

• Testing to the Black Mura standard in TrueTest ™

• Comparing the Black Mura method to Radiant Mura test methods

• Black Mura as part of a more elaborate display test


53 S E E T H E D I F F E R E N C E © 2015 Radiant Vision Systems, LLC. All Rights Reserved Quality-Driven: Automotive Display Testing

THANK YOU

If you have questions regarding this topic or presentation, please contact us at [email protected]

quality driven...2015/10/13 · see the difference 1 quality-driven: automotive display testing ©...

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